We assessed 77 twin pregnancies, comprising complete hydatidiform mole (CHM) and healthy co-twin, to ascertain the risks to the mother and baby of continuing the pregnancy, versus termination. 24 women with histologically confirmed CHM and healthy co-twin pregnancies decided to have a termination. 53 women continued with their pregnancies, though two had to have terminations because of severe pre-eclampsia, and 23 spontaneously aborted (<24 weeks' gestation). 28 pregnancies lasted 24 weeks or more, resulting in 20 livebirths. Chemotherapy to eliminate persistent gestational trophoblastic disease (pGTD) was required in three of 19 women (16%; 95% CI 3-39) who terminated their pregnancies in the first trimester, and in 12 of 58 (21%; 95% CI 11-33%) who continued their pregnancies. CHM and healthy co-twin pregnancies have a high risk of spontaneous abortion, but about 40% result in livebirths, without significantly increasing the risk of pGTD.